Hydraulically powered wrenches are known in the art. In one existing system, a linear hydraulic piston turns a link plate, which in turn causes a lever arm having a spring-loaded pawl thereon to rotate and thereby impart torque to a fastener having teeth that engage the pawl. Spring action may then be used to transmit force through the drive train of the apparatus to reset the position of the piston. Thus, hydraulic force to the piston may be released, whereupon a spring may force the link plate and lever arm to retrace the motion undertaken during the piston stroke. During the spring-forced movement of the link plate and lever arm, the pawl reverses its motion with respect to the teeth on the driven member using a conventional ratcheting function. Once the spring driven stroke is complete, the entire mechanism is ready for the next piston power stroke to turn the driven member again. The above cycle may be repeated as many times as needed to complete a tightening function or any other desired operation.
A problem with the above approach is that spring-driven repositioning systems tend to be slow. Moreover, the piston-repositioning spring may weaken over time. Once this occurs, the repositioning spring may become incapable of properly repositioning the linkage to be powered by the piston, thus rendering the overall apparatus inoperable. Moreover, repairing or replacing the spring is expensive and time consuming.
Another approach to using hydraulic power for high-torque wrenches involves providing two fluid inputs to a cylinder, one on either side of the piston. A first fluid inlet at a proximal end of the cylinder is used to force the piston in a first direction to deliver tightening force through the linkage (discussed above) to a driven member. The equipment is moved in the reverse direction to reset the pawl and the position of the piston by providing pressurized fluid to a second fluid inlet to the cylinder at the distal end of the cylinder to force the piston into a retracted position.
However, this approach also presents drawbacks. Providing and servicing the described second fluid inlet to the cylinder is cumbersome and expensive. Moreover, when operating within a confined space, extending pressurized fluid tubes to the second fluid inlet tends to be cumbersome and to inhibit optimal operation of a hydraulic wrench under such demanding circumstances. Further, to provide an opening into the area at the distal end of the cylinder typically requires a bore be drilled through an outer and inner cylinder, so that the outer cylinder can be plugged, causing the fluid to flow from the space between the two, into the inner cylinder. In many instances, the high pressure of the hydraulic fluid causes the plug to pop out of the outer cylinder, which in turn causes hydraulic fluid to leak, and the device to become essentially inoperable.
Accordingly, there is a need in the art for an improved system and method for restoring a hydraulic piston to an initial position.